Gain scaling of short-wavelength plasma-recombination lasers

The theoretical Z-to-the-7.5-power dependence of the small-signal gain of plasma-recombination lasers on the ionization stage Z of the laser species, while implying a straightforward development of short-wavelength lasers, is thought to be significantly larger than the experimentally achieved gain scaling. A new analysis, which incorporates a simple experimental parameter representing the efficiency of populating the upper level at a given plasma electron density, gives a gain scaling with ionization state (Z to the 4.5 power) that is more consistent with experiments. It also reveals the need for better experimental control of the ion-production and electron-ion-recombination processes in attempting to construct lasers of this type.